In general, existing positioning systems needed to provide LBS's (Location Based Services) can be mostly classified into network-based schemes that use RF (Radio Frequency) signals from cell phone towers, schemes that use signal strengths of AP (Access Point) or Bluetooth beacons, and schemes using GPS signals.
Although some of these schemes are suitable in an outdoor environment where RF signals can be received well, they may not be suitable for radio shadow areas such as some indoor spaces, and may require expensive transmitters and receivers as well as extra relaying stations. In the case of schemes that use AP's (Access Point) and Bluetooth beacons, the scanning frequency of many personal devices are not frequent enough, and users may have to turn on the Wi-Fi or Bluetooth function of the device.
In indoor spaces where GPS signals can't reach easily, it's very difficult to provide information of facilities or objects, the best way of traveling, navigation or directories based on user's location. Measuring received signal strength of different signaling devices that have different signal strength can lower the accuracy and requires periodic surveys of AP's and beacons in the area.
With regards to similar positioning systems, a reference called “Three-dimensional spatial localization apparatus using sound wave or ultrasonic wave propagation time” in Korea Patent Publication No. 10-2005-0095401 exists.